The invention relates to enhancing the effect of vaccines in animals, such as domestic, sport, or pet species, and humans. More particularly, the invention relates to the use of interleukin-2 (IL-2) as an adjuvant with vaccines.
The use of vaccines to prevent diseases in humans, farm livestock, sports animals and household pets is a common practice, and considerable effort has been, and is being, made to extend this practice to cover a more extensive array of diseases to which these patients are subject. For example, the use of rabies vaccine in animals is by now commonplace, and efforts are being made to obtain suitable vaccines to immunize animals against other diseases.
One problem that frequently is encountered in the course of active immunization is that the antigens used in the vaccine are not sufficiently immunogenic to raise the antibody titer to sufficient levels to provide protection against subsequent challenge or to maintain the potential for mounting these levels over extended time periods. Another problem is that the vaccine may be deficient in inducing cell-mediated immunity which is a primary immune defense against bacterial and viral infection. Notorious among such "weak" animal vaccines are those constituted from inactivated Haemophilus pleuropneumoniae (Hpp) (which is associated with respiratory disease in pigs).
In order to obtain a stronger humoral and/or cellular response, it is common to administer the vaccine in a formulation containing an adjuvant (immunopotentiator), a material which enhances the immune response of the patient to the vaccine. The most commonly used adjuvants for vaccines are oil preparations and alum. The mechanisms by which such adjuvants function are not understood, and whether or not a particular adjuvant preparation will be sufficiently effective in a given instance is not predictable.
Accordingly, there is a need for additional effective adjuvant preparations which are suitable for potentiating vaccines for animals in general, including humans and other mammals. It has now been found that human IL-2 (hIL-2) is useful in this regard.
There is considerable background information available with respect to the biological activity of hIL-2. hIL-2 can be obtained from the supernatant of concanavalin-A (ConA) stimulated spleen cells or, presently, using recombinant technology, and has several measurable activities in vitro. First, it is a T-cell growth factor as measured by, for example, thymidine uptake when hIL-2 is added to cultures of cytotoxic or helper T-cell lines. It is mitogenic with respect to adult thymocytes, and stimulates a cytotoxic cell response (e.g., lymphokine-activated-killer (LAK) cell). It has also been shown to replace helper T-cells in athymic murine spleen cell cultures (Watson, J., et al., Immunological Rev. (1980) 51:257-278). Specifically, in the presence of IL-2 and antigen, specific T helper cells are generated which are able to contribute to antibody responses. Presumably this occurs because IL-2 is involved in the antigen-dependent maturation of helper T-cells in these nude mouse spleen cultures.
IL-2 has also been shown to directly affect B cells in vitro. Both proliferation and IgM and IgG secretion are enhanced by IL-2 in populations of purified, activated B cells (Mingari, M. C., et al., Nature (1984) 312:641; Mittler, R., et al., J. Immunol. (1985) 134:2393-2399; Muraguchi, A., et al., J. Exp. Med. (1985) 161:181-197).
How these in vitro activities translate into a specific in vivo mechanism for mounting an immune defense is not clear. However, with respect to such in vitro studies, cross-reactivity among species of various IL-2s has been studied. For example, Redelman, D., et al., J. Immunol. Meth. (1983) 56:359-370) show that hIL-2 supports activated T lymphocytes derived from rabbit and mouse to approximately the same extent as they are supported by the endogenous forms of IL-2. Ruscetti, F. W., et al., Blood (1981) 57:379-393 were the first to demonstrate the ability of hIL-2 to behave as a growth factor, not only for human T-cells, but also peripheral blood lymphocytes or splenocytes from other primates, horse, guinea pig, cat, rat, and mouse. Carter, J., et al., (Fed. Proc. (1985) 44:1290) disclose the ability of hIL-2 to enhance the development and maintenance of bovine cytotoxic lymphocytes in vitro.
Doyle, M. V., et al., J. Bio. Resp. Mod. (1985) 4:96-109 reports in vitro lymphocyte proliferation studies that compared the activities of native hIL-2 and a recombinant form of IL-2 on human and animal lymphocytes. The native IL-2 and recombinant IL-2 exhibited the same range of activity on animal cells.
Some in vivo data are also available. The activity of IL-2 in vivo has been shown to restore immunocompetence in nude mice in response to heterologous erythrocytes (Stotter, H., et al., Eur. J. Immunol. (1980) 10:719-722). There is information concerning cross-species reactivity, as well. Reed, S. G., et al., J. Immunol. (1984) 133:3333, disclosed the ability of hIL-2 to reconstitute spleen cell responses in mice infected with a parasitic protozoan, and Farrar, J. J., et al., Immunol. Rev. (1982) 63:158, showed that in vivo injection of IL-2 of human origin stimulates the splenic T-cells in nude mice. Fong et al., Vet. Immuno. & Immunopathol. (1986) 11:91-100 discloses the response of bovine and porcine peripheral blood mononuclear cells to human rIL-2. Stott et al., Vet. Immunol. and Immunopathol. (1986) 13:31-38 disclose that human rIL-2 augments in vitro the blastogenesis of bovine and porcine lymphocytes. Kawamura et al., J. of Exp. Med. (1985) 162:381-386 disclose that immunization with antigen and IL-2 in vivo overcomes Ir gene low responsiveness in mice. McFeeters and Nadler, Fed. Proc. 45(3) 633 (presented Apr. 13-18, 1986) disclose enhancement of antibody responses to protein antigens by administering rIL-2. Dr. Thompson at the University of Washington is investigating that IL-2 may boost vaccines (Gen. Tech. News, June 1986).
In summary, it is known that IL-2 behaves in some manner in vivo to mediate a successful immune response, including a response to a specific antigen, and in vitro studies have shown that cross-species reactivity of hIL-2 is very diverse (prior in vivo cross-species studies have involved only murine subjects for hIL-2). However, because the mechanism of involvement of hIL-2 in the immune response is not understood, it is not possible to predict the behavior of hIL-2 in boosting a protective immune response to an antigen administered as a vaccine to animals or humans. Accordingly, there is no suggestion in the art that hIL-2 could successfully be used as an adjuvant in vaccines. This is the contribution of the present invention.